In a statement, United Airlines confirmed that the plane made an emergency landing at 12:38 p.m. local time.

“United flight 1175 traveling to Honolulu from San Francisco landed safely after the pilots called for an emergency landing because of an issue with the #2 engine. Our pilots followed all necessary protocols to safely land the aircraft," they said in a statement.

It is believed that the cowling — the covering over an airplane's engine — became loose and then fell away during the flight.

The plane was met by emergency service vehicles, United said. They added that the airline "is fully cooperating" with investigations by the National Transportation Safety Board and Federal Aviation Administration.

Rose Troup Buchanan is a reporter for BuzzFeed News and is based in London.